1. Field of the Invention
The present invention relates to a hand position detecting device for detecting the position of a hand (or a pointer) and an electronic timepiece.
2. Description of the Related Art
There has been hitherto developed a hand position detecting device for detecting the position of a hand to check whether the hand is positionally displaced or not (for example, see JP-A-2009-85674).
In a conventional hand position detecting device, a second hand and a minute hand are detected as follows, for example. That is, one through hole is provided in a minute hand wheel rotating interlockingly with the minute hand, and one through hole and an elongated hole extending over a fixed angle range are provided in a second hand wheel rotating interlockingly with the second hand. Furthermore, the hands and gearwheels are assembled with one another so that the through hole of the minute hand wheel and the through hole of the second hand wheel are overlapped with each other at a detection position at a specified time (for example, every hour 55 minute 00 second). A photointerruptor or the like is made to detect overlap or non-overlap between the through hole of the minute hand wheel and the through hole or elongated hole of the second hand wheel from the specified time for a fixed time period for which the minute hand is stopped (for example, ten seconds), thereby judging whether position displacement occurs between the minute hand or the second hand or not.
For example, by providing the elongated hole of the second hand wheel from a position which is far away from the through hole by ten steps, after the overlap between the through holes is detected at a specified time, the overlap of the through holes is not detected while the second hand wheel is rotated by two, four, six and eight steps, but the overlap between the through hole of the minute hand wheel and the elongated hole of the second hand wheel is detected at the position corresponding to the ten steps when there is no positional displacement in the hands. On the other hand, when there is any positional displacement in the second hand or the minute hand, the detection pattern from the specified time till 10 steps as described above is not obtained. Accordingly, the presence or absence of the positional displacement in the minute hand or the second hand can be determined by judging whether this detection pattern is obtained or not.
In a process of fabricating an electronic timepiece, after all gear wheels are moved to reference positions, the hands are assembled so as to be oriented in predetermined positions (called as hands mounting). In this case, the hands may be assembled while slightly positionally displaced. The conspicuous degree of assembling error of each hand is not equal among all the hands, and the minute hand is particularly more conspicuous in property. This is because the minute hand has a small rotational angle per step and has such a length as to be lean to scales on a dial. For example, in a case where the minute hand is assembled with a displacement of “−2°”, the minute hand is set to be displaced from the scale of twelve o'clock on the dial by “−2°” when the time of the timepiece is “00 minute 00 second”, and the minute hand is set to be just overlapped with the scale of twelve o'clock when the time of the timepiece is “00 minute 20 second”. Visually comparing these states, a user recognizes the assembling error of the minute hand.
With respect to a conventional electronic timepiece having no hand position detecting mechanism, when an assembling error of the minute hand as described above occurs, the error can be eliminated by adjusting the reference position of the minute hand wheel. That is, even when the minute hand is assembled with a displacement of “−2°”, the position at which the minute hand wheel is rotated from the above state by two steps is regarded as the reference position of the minute hand wheel, whereby the minute hand can be set so that the time at which the minute hand is just overlapped with the scale of twelve o'clock on the dial is equal to the counted time “00 minute 00 second”.
However, with respect to an electronic timepiece having the conventional hand position detecting mechanism described above, the assembling error of the minute hand cannot be eliminated by adjusting the reference position of the minute hand wheel. For example, it is assumed that the minute hand is assembled to be displaced from the scale of twelve o'clock by “−2°” when the through hole of the minute hand wheel is overlapped with the detection position, and also it is assumed that the specified time at which the detection of the through hole is performed is adjusted and set to “59 minute 40 second” in conformity with the displacement of “−2°” of the minute hand. In this case, at the specified time, the through hole of the minute hand wheel is overlapped with the detection position, and also the second hand wheel is set so that the position corresponding to “40 seconds” is overlapped with the detection position. Accordingly, when the detecting operation is executed from the specified time every two steps per ten seconds, the detection pattern such as detection-non-detection -non-detection-non-detection-non-detection-detection of transmitted light as described above is not obtained, and for example, there is obtained a detection pattern with which it cannot be specified which position the second hand wheel is located at like detection-detection-detection-detection -detection-detection of transmitted light because the elongated hole of the second hand wheel is overlapped with the detection position. Accordingly, in the electronic timepiece having the conventional hand position detecting mechanism, when the assembling error of the minute hand occurs, the minute hand must be detached and then mounted with high precision again.
The present invention provides a hand position detecting device and an electronic timepiece that can perform hand position detection according to the same algorithm even when the timing of the hand position detection is varied due to assembling error of a minute hand or the like.